Overload protective device



Oct. 18, 1949. w, SHLWELL, JR 2,484,863

OVERLOAD PROTECTIVE DEVICE Filed Aug. 12, 1945 2 Sheets-Sheet l 2 2 COME/NATION I I CONTACTMAD! 4r 711/5 rosszs omz Oct. 18, 1949. w. E. STILWELL, JR 2,484,863

OVERLOAD PROTECTIVE DEVICE Filed Aug. 12, 1943 2 Sheets-Sheet 2 INVENTOR ILL\AM E.5TILWELL, R

TTORNEY Patented Oct. 18, 1949 OVERLOAD PROTECTIVE DEVICE William E. Stilwell, Jr., Cincinnati, Ohio, assignor to John B. Pierce Foundation, New York, N. Y., a corporation of New York Application August 12, 1943, Serial No. 498,273

2 Claims. (01. 200-87) This invention relates to overload protective devices and particularly to overload devices actuated by increase in magnetic flux about an electricity conductor when the current carried by such conductor is increased.

An object of the invention is to provide means responsive to predetermined overload conditions to actuate a circuit breaker, whereby apparatus may be protected against the efiects of overloads.

It is an object of the invention to provide a magnetic overload circuit breaker which may be attached to a conductor of thecircuit to be protected, at any convenient location, without disconnecting or breaking said conductor.

It is an object of the invention to provide a circuit breaker which is of simple, inexpensive construction, and may be manufactured to small size and light weight.

According to preferred embodiments of the invention my improved circuit breaker comprises a substantially U-shaped strap or bar of soft iron or like magnetically responsive material, said strap having a body member defining an aperture through which the conductor of the circuit to be protected may extend, and wing portions extending respectively in opposite directions, from each of the legs of the U. When exposed to magnetic flux, said body becomes a magnet, each of the wing portions forming a pole thereof. Secured to one of the poles, and extending in the direction of the other, is a polepiece extension; and upon said extension there is pivoted a soft-iron armature having a free end extending beyond the end of said pole-piece extension to overlie the opposite pole of the strap in spaced relationship therewith.

A non-magnetic housing encloses the pole-piece extension and its associated armature, and a (spring, with means for adjusting the tension thereof, urges the armature in the direction of the pole-piece extension. Under normal current conditions within the circuit, the induced magnetism is not sufficient to overcome the air gap between the armature and the magnetic pole of the body which it overlies; under abnormal, i.'e., high current in the conductor, the increased magnetic efiect overcomes the magnetic reluctance of the air gap and the armature tilts toward the pole of the body member.

Such movement of the armature may be employed to close, or open if desired, the circuit Fig. 2 is a plan view taken from the underside of the structure of Fig. 1;

Fig. 3 is a transverse sectional elevation taken on lines 33 of Fig. 1;

Fig. 4 is a diagrammatic Wiring circuit incorporating the overload protector and circuit breaker associated therewith;

Fig. 5 is an elevation partly insection of an other preferred embodiment of the invention;

Fig. 6 is a schematic wiring diagram showing the manner in which the circuit breaker of Fig. 5 may be employed; and

Fig. 7 is a load-deflection diagram showing the operating characteristics obtained by combining a leaf spring and a loop spring to obtain toggle action of the circuit breaker.

Referring to the drawings, my improved circuit breaker Iii comprises a strap or bar of soft iron or like magnetically responsive material having a U-shaped body H, with sidewardly extending wing portions 12, iii. The body H receives a conductor M of the circuit to be com trolled and is in electrical contact therewith. Electrical contact may be effected by the removal of a suitable portion of the insulation of the conductor M, to bring the same into contact with the body I I, or through the agency of the pointed set screw l5 which penetrates the insulation and makes contact with the conductor. A n0nmagnetic sleeve [6 held in position by a nonmagnetic cotter pin or the like confines the com ductor within the passage through the body struc ture II.

The structure It, l2, l3 becomes magnetized by the magnetic flux surrounding conductor M during the passage of electricity therethrough, and the wings I2, 43, form the poles of said strUcture. Secured to the wing I2 is a pole-piece extension of iron provided at its outer end with a rivet l8 which serves to pivotally secure to pole-piece extension H a magnetically responsive, preferably dip and medially pivoted ture 20.

A shim 2| of non-magnetic material is applied to the underside of armature 26 at one end thereof, to space the armature from the pole piece extension I! except at the rivet l8. Desirably, see Fig. 1, the armature 2%] is eccentrioally mounted, in that the end 293a thereof is longer than that portion of armature 2a in operative association with the pole-piece extension H. The end 20a of armature 2t overlies the pole 53, in spaced relation therewith, it being understood that the illustrated spacing is greatly exaggerated.

A non-magnetic housing 22 provides an enc1osure, and may be removably secured to the wings l2, l3 by screws. The housing see 8, prevents rotation of armature 21! in the plane of pole-piece extension ll.

Insulatedly carried by the said housing 22 is a terminal 23 having a contact 23a. Secured to the armature 2B is a cooperating contact 24.

The armature is adjusted for varying values of overload by means of suitable resilient means, such as the leaf spring 25, one end of which is secured to or adjacent the free end of the armature portion 29a, as shown, the regulation of the leaf spring being had by adjustment of the set screw 26, which is disposed over-center, i. e., the left of the rivet it upon which the armature 20 is pivoted, and accordingly upon any predetermined adjustment of the set screw 25, the leaf spring serves to resiliently bias the armature 20 toward engagement with the pole piece extension ll.

Cooperating with the armature 251 and its adjusting leaf spring 25 there is provided suitable means for precluding chattering by suitable resilient means, serving dually to effect snap action to the movement of the armature under the condition of effective overload in excess of the setting of the set screw 26, exemplified by the employment of the loop or U-shaped spring 27, mounted in over-center relation with respect to the center of the free end 2M of the armature 20, as by lodging one of the ends of the spring in the indicated recess formed in the inner face of the lateral wall of the insulating housing 22 and its other end lodged in a recess formed at the free end of the armature portion 23a, such second-named recess being located with respect to such first-named recess to normally bias the armature 2!] in direction of rotation coincidental with the direction of rotation effected by the bias of the spring 25.

Fig. '7 is a typical load-deflection diagram showing the load-deflection characteristics of the loop spring and the leaf spring, and of the combined action of said springs. that electric contact is made ata toggle point wherein the deflection of the spring assembly to throw the armature 20 occurs spontaneously without additional load application.

Fig. 4 shows schematically an electric wiring diagram. Load L may be broken by a circuit breaker 30 actuated by the device above described, illustratively a single pole type in which a shorting bar 31 is carried by a toggle mechanism 32. A solenoid 33 acts upon core 34 to draw the core and associated shaft 35 to the right when the solenoid is energized, thereby opening the circuit in conductor Hi. A conventional overthrow spring 33 holds circuit breaker 30 in either open or closed position and a manual reset 3'! is a conventionalized means of resetting the circuit breaker.

A switch 38 is typical of any switch suitable to energize the solenoid 33 for remote control of load circuit L.

The overload protector may be disposed about the conductor l4 by removing cap 22, extension ll, sleeve l5 and cotter pin, and reassembling the same after the conductor has been passed through the body i i. To terminal 23 a conductor 39 connects with solenoid 33. A conductor 40 completes the solenoid circuit in the load circuit L. With the overload protector It in open circuit position, conductors 39, 49 are not in connection with the solenoid 33; closing push button 38 will energize solenoid 33 to bring the overthrow spring 36 through its dead center position to hold the switch 3! in open circuit position. The circuit breaker 30 forms no part of the present invention, and

It W111 be noted no showing of automatic circuit restoring apparatus has been made.

In the present invention, the magnetic flux about the conductor l 4 during current flow therethrough assumes a path from pole IE to pole-piece extension I! which is in contact therewith, and thence to armature 29. The shim between extension H and armature 20 introduces an air gap which restricts the flow of magnetic flux from extension I! to armature 23 except where the armature and the pole-piece extension may be in physical contact. The path of magnetic flux, with respect to the armature- 23, is therefore primarily from the pole-piece extension I! to the end portion 20a of the armature 20, and thence to the pole [3.

Under ordinary conditions the strength of magnetic flux about the conductor 54 is insufficient to overcome the gap between the armature end Ella and the pole i3 whereupon the magnetic attraction of the pole-piece extension l l for the armature 20, plus the bias of spring 25, maintains the armature in its Fig. 1 position, with the contacts 23, 23a in open circuit status. However, when the strength of the magnetic flux about the conductor 14 increases with an increase in the current flow through conductor M, the magnetism will attain such a value that the attraction of the armature end 26a for the pole i3 will overcome the magnetic reluctance introduced by the air gap and the armature 28 will be rotated sharply clockwise of Fig. 1 thereby closing the circuit between the contacts 23a and 24 and energizing the solenoid coil 33 to actuate the circuit breaker 20. With the cessation of current flow in the load circuit L, there is no longer a magnetic flux surrounding the conductor 14 and. the spring 25 returns the armature to the Fig. 1 position thereby breaking the auxiliary circuit to the solenoid The embodiment illustrated in Fig. 5 typical of an application in which the solenoid coil of circuit breaker 3% must be continuously energized in order to maintain a closed circuit. In Fig. 5, the structure of the overload protective device I!) is substantially the same except that the contact 24 is placed upon the end 20:: of armature 20, and contact 23a is appropriately changed in location.

The spring 25 holds the contacts in closed circuit position. Under an overload condition the armature 20 is rotated to open the circuit. The manual control switch 42 is normally closed, and with the overload protector ii) in series connection therewith, opening the contacts 23a, 24 opens the control circuit to the circuit breaker 38a, and the.

load circuit L is opened.

Whereas I have described my invention by reference to specific forms thereof, it will be understood that many changes and modifications may be made provided they do not depart from the scope of the claims.

I claim: 1. In an overload protector, a magnetically responsive structure comprising a substantially H a magnetically responsive armature pivotally supported upon said magnetically responsive extension for rotation toward the other of said extensions and having an end overlying said other extension in spaced relationship therewith, resilient means normally biasing said armature away from said other extention, an electric contact on said armature, a second electric contact operatively associated with said first-named electric contact, and means dually precluding chattering of said magnetically responsive armature under the condition of flow of electric current through said conductor of a value less than overload and cooperating with said resilient means under the condition of overload of such electric current to accelerate said magnetically responsive armature to connect said contacts with one another.

2. In an overload protector, a substantially U-shaped bar of soft iron or like magnetically responsive material adapted to embrace a conductor of an electric circuit, the opposing ends of said bar being turned outwardly in the same plane to serve as magnetic poles when the bar is exposed to magnetic flux surrounding the conductor during passage of current therethrough, one of said ends having an extension directed toward but spaced from the opposite pole; a magnetically responsive armature pivotally mounted upon said extension and having one end overlying said extension in spaced relationship therewith, the center portion of said extension being in magnetic relation with one of the poles and having its opposite end overlying the opposite pole in spaced relationship therewith; means for resiliently maintaining the said spaced relationship; electric contact means controlled by said armature; a second contact means cooperating with said first contact means; and means dually precluding chattering of said armature under the condition of flow of electric current through said conductor of a value less than overload and cooperating with said resilient means under the condition of overload of such electric current to accelerate said magnetically responsive armature to connect said contacts with one another.

WILLIAM E. STILWELL, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 728,752 Naphtaly et al May 19, 1903 850,205 Bergman Apr. 16, 1907 890,697 Noeggerath June 16, 1908 1,220,813 Barrow Mar. 27, 1917 1,930,528 Marthens Oct. 17, 1933 1,934,264 Hefner Nov. 7, 1933 1,983,026 Greenleaf Dec. 4, 1934 2,075,499 Bush et al Mar. 30, 1937 FOREIGN PATENTS Number Country Date 401,393 Germany Sept. 4, 1924 

